1. Field of the Invention
The present invention relates to cryogenic fluids. In another aspect, the present invention relates to storage apparatus for and methods for processing, transporting and/or storing cryogenic fluids. In even another aspect, the present invention relates to methods and apparatus for processing, transporting and/or storing liquified natural gas (“LNG”).
2. Description of the Related Art
Interest in the use of liquified natural gas (LNG) as a fuel for motor vehicles has increased dramatically in recent years. Entire fleets of government and industrial vehicles have successfully been converted to natural gas. Some privately-owned vehicles have been converted as well. Congress has passed an energy bill that requires increased use of alternative fuels in government and private fleets. Several factors have influenced this increasing use of LNG as a fuel in motor vehicles. LNG is relatively inexpensive. In addition, it burns very cleanly, making it much easier for fleets to meet more restrictive pollution emission standards. And, in terms of reducing dependence on imported oil, natural gas is abundantly available in the United States.
Most conveniently, natural gas is transported from the location where it is produced to the location where it is consumed by a pipeline. However, given certain barriers of geography, economics, and/or politics, transportation by pipeline is not always possible, economic or permitted. Without an effective way to transport the natural gas to a location where there is a commercial demand, the gas may be burned as it is produced, which is wasteful.
Liquefaction of the natural gas facilitates storage and transportation of the natural gas (a mixture of hydrocarbons, typically 65 to 99 percent methane, with smaller amounts of ethane, propane and butane). When natural gas is chilled to below its boiling point (in the neighborhood of −260° F. depending upon the composition) it becomes an odorless, colorless liquid having a volume which is less than one six hundredth ( 1/600) of its volume at ambient atmospheric surface temperature and pressure. Thus, it will be appreciated that a 150,000 cubic meter LNG tanker ship is capable of carrying the equivalent of 3.2 billion cubic feet of natural gas.
When LNG is warmed above its boiling point, it boils reverting back to its gaseous form.
The growing demand for natural gas has stimulated the transportation of LNG by special tanker ships. Natural gas produced in remote locations, such as Algeria, Borneo, or Indonesia, may be liquefied and shipped overseas in this manner to Europe, Japan, or the United States. Typically, the natural gas is gathered through one or more pipelines to a land-based liquefaction facility. The LNG is then loaded onto a tanker equipped with cryogenic compartments (such a tanker may be referred to as an LNG carrier or “LNGC”) by pumping it through a relatively short pipeline. After the LNGC reaches the destination port, the LNG is offloaded by cryogenic pump to a land-based regasification facility, where it may be stored in a liquid state or regasified. If regasified, the resulting natural gas then may be distributed through a pipeline system to various locations where it is consumed.
Of the known liquid energy gases, liquid natural gas is the most difficult to handle because it is so intensely cold. Complex handling, shipping and storage apparatus and procedures are required to prevent unwanted thermal rise in the LNG with resultant regassification. Storage vessels, whether part of LNG tanker ships or land-based, are closely analogous to giant thermos bottles with outer walls, inner walls and effective types and amounts of insulation in between.
LNG storage tanks in the United States have heretofor been built mostly above the ground with some frozen pit facilities properly characterized as mostly above the ground. Most such tanks have been enclosed by a low rising earthen dike. Such dikes were sized and placed to enclose an area and volume at least as great as the storage capacity of the largest tank (if not all of the tanks) within the diked area.
In addition, National Fire Protection Association (NFPA) guidelines (NFPA 59A, Para 108) for spill containment require impounding areas that hold the entire LNG capacity of the station in the event of a catastrophic spill. Furthermore, in accordance with NFPA guidelines, electrical controls must either be designed for explosion-proof conditions or be situated in designated safe areas outside of the impoundment area generally several hundred feet away. As explosion-proof controls are costly, the latter option is preferable.
Thus, LNG to be regasified is generally pumped to a heating device situated outside the impoundment area several hundred feet away in a designated safe area.
In spite of the presence of insulation, storage tanks will still cool if not freeze any ground in direct contact with the tank. Thus, an electrical heating element is placed in the ground to counter any cooling by the tank.
A number of patents relate to the processing, transporting, and storing of LNG.
U.S. Pat. No. 3,675,431 issued Jul. 11, 1972 to Jackson, discloses a partially submerged offshore storage tank for liquified energy gases. That patent described an insulated tank which was prefabricated, floated to a suitable offshore site and then sunk until its submerged base rested on the floor of the sea. An upper above-the-water domed metal cylinder extended from a concrete base. Insulation lined the interior of the tank. A thin and flexible membrane inside the insulation provided the required liquid tight interior lining of the tank. The insulation lining the submerged portion of the tank was said to be thinned, so that a layer of ice formed around the outside of the concrete base when the tank was filled with liquified gas. In accordance with the invention claimed in the patent, the ice layer supposedly acted as an outer seal for the submerged concrete.
U.S. Pat. No. 3,727,418, issued Apr. 17, 1973, to Glazier, discloses an LNG storage facility having an insulated interior membrane. A balancing fluid, said to be isopentane (2-methyl butane) transferred hydrostatic pressure from surrounding ambient water to the LNG contents.
U.S. Pat. No. 3,828,565, issued Aug. 13, 1974 to McCabe, discloses an insulated buoyant tank moved telescopically up and down in a larger receiver tank containing seawater, oil or other liquid in accordance with the quantity of LEG at atmospheric pressure stored therein from time to time.
U.S. Pat. No. 4,041,722, issued Aug. 16, 1977, to Terlesky et al., discloses an impact resistant tank for storing cryogenic fluids, includes an inner metal tank having a metal side wall and a metal bottom and a concrete outer wall around the inner metal wall and having reinforcement therein to resist impact loads thereon, and to serve as a secondary containment for the cryogenic fluid. A multiplicity of dual purpose separating plates not only ensure a rigid structure for the tank, they effectively divide up the tank into separate storage compartments, thus minimizing leakage to that compartment with a fracture.
U.S. Pat. No. 4,209,267, issued Jun. 24, 1980, to Gnaedinger, proposes an improvement over the traditional earthen dike system around LNG storage tanks. Specifically, the storage system comprises a dike, impounding wall or drainage channel constructed of compacted earth, concrete, metal and/or other suitable substance surrounding an aboveground steel insulated tank used to store the liquefied gas. A drop shaft is used to communicate the diked area with an underground tunnel for temporary accumulation and subsequent safe disposal of liquid which has escaped from the storage tank.
U.S. Pat. No. 4,374,478, issued Feb. 22, 1983, to Secord et al., discloses tanks for land storage of liquefied gas at low temperature at or above atmospheric pressure. The invention provides a storage tank of the kind in which the walls are formed by a multiplicity of connected, parallel, part-cylindrical lobes presenting outwardly convex arcuate surfaces, which is characterized in that the side and end walls thereof are provided by a single tier of connected lobes, in that said lobes extend in one common direction over the tank, in that the end walls of the tank comprise part-spherical knuckles closing off the ends of the part-cylindrical lobes, and in that a separating plate is provided at each lobe connection to strengthen the tank against internal pressure and to divide it into separate storage compartments.
U.S. Pat. No. 5,682,750, issued Nov. 4, 1997, to Preston et al., discloses a portable self-contained delivery station for liquid natural gas (LNG) is provided on a movable skid frame and equipped with an instant-on delivery system which may initiate LNG delivery immediately to a use vehicle. The skid is equipped with a spill containment feature such that the LNG may be contained in the event of spillage. A variable speed pump both controls LNG dispensing and saturation levels of the stored LNG. The pump is submerged in a sump tank which is separate from the bulk storage tank. The sump tank is flooded with an amount of LNG such that the pump is submerged. Delivery of LNG may thus occur instantly, without pre-cooling of the pump or associated meter.
U.S. Pat. No. 6,640,554, issued Nov. 4, 2003, to Emmer et al., discloses a portable self-contained liquid natural gas (LNG) dispensing system is housed in a container featuring opposing side and end walls and a bottom panel. The container is divided into a ventilated portion and a covered portion. A roof is over the covered portion while the ventilated portion features an open top. A bulk tank positioned within the container contains a supply of LNG with a head space thereabove and a pump is submerged in LNG within a sump that is also positioned within the container and communicates with the bulk tank. The container is lined with stainless steel sheets to define a containment volume that is capable of holding the entire supply of LNG in the bulk tank. A vent valve communicates with the head space of the bulk tank and is positioned under the open top of the ventilated portion of the container. The electric controls are positioned on the lower portion of the end wall of the covered portion of the container so as to be located in accordance with the appropriate safety guidelines.
All of the patents cited in this specification, are herein incorporated by reference.
However, in spite of the above advancements, there still exists a need in the art for apparatus and methods for processing, transporting, and/or storing LNG.
This and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.